1. Field of the Invention
The present invention relates to a piezoelectric device for use in an inkjet recording head, a process for producing the piezoelectric device, and an inkjet recording head using the piezoelectric device.
2. Description of the Related Art
Currently, piezoelectric devices constituted by a piezoelectric film and electrodes are used as, for example, actuators installed in inkjet recording heads, where the piezoelectric film expands and contracts according to increase and decrease in the strength of an electric field applied from the electrodes to the piezoelectric film in a predetermined direction. For example, perovskite oxides such as PZT (lead titanate zirconate) are known as materials suitable for the piezoelectric film.
When the vector direction of the spontaneous polarization axis in the piezoelectric film coincides with the direction of the electric field applied to the piezoelectric film, the expansion and contraction according to increase and decrease in the strength of the electric field effectively occur, so that the piezoelectric constants become great. It is most preferable that the direction of the spontaneous polarization axis in the piezoelectric film completely coincide with the direction of the electric field applied to the piezoelectric film. In addition, in order to suppress the variations of the ink discharge amount, it is desirable that the variations in the piezoelectric performance of the piezoelectric film over the surface of the piezoelectric film be small. In consideration of the above circumstances, it is desirable that the piezoelectric film have high degree of crystal orientation.
For example, Japanese Unexamined Patent Publication No. 2004-186646 (hereinafter referred to as JPP 2004-186646) discloses a technique of growing a PZT film which is preferredly oriented along the (001) plane on a surface of a lower electrode of noble metal containing titanium, where the lower electrode is formed by concurrent sputtering of titanium and noble metal such as platinum, and titanium is insularly precipitated on the surface of the lower electrode.
In addition, Japanese Unexamined Patent Publication No. 2004-262253 (hereinafter referred to as JPP 2004-262253) discloses that it is possible to form a PZT film having high degree of crystal orientation by using a MgO substrate.
According to the technique disclosed in JPP 2004-186646, it is possible to form a PZT film exhibiting crystal orientation. However, as indicated in the embodiments 1 to 5 in JPP 2004-186646, the values of the piezoelectric constant d31 of the PZT films obtained according to the embodiments 1 to 5 in JPP 2004-186646 range from 122 to 138 pm/V (i.e., −122 to −138 pC/N), and no PZT film having the piezoelectric constant d31 of 150 pm/V or greater is reported in JPP 2004-186646.
On the other hand, since the MgO substrate, which is required to be used in the technique disclosed in JPP 2004-262253, is expensive, the use of the technique disclosed in JPP 2004-262253 increases the manufacturing cost.
In addition, according to the techniques disclosed in JPP 2004-186646 and JPP 2004-262253, it is basically necessary that the film-formation temperature at which the PZT film is formed be 600° C. or higher, as indicated in the embodiments 1, 2, 4, and 5 in JPP 2004-186646. In addition, the lowest film-formation temperature indicated in JPP 2004-186646 is 580° C. (in the embodiment 3 in JPP 2004-186646). Thus, it is conjectured that the film-formation temperature is required to be 580° C. or higher according to the techniques disclosed in JPP 2004-186646. However, when the PZT film is formed at high temperatures, lead loss can occur in the PZT film, so that the piezoelectric performance can deteriorate.